It really depends on which coin it is. Is it a US silver dollar or dime? There is a big difference. Is it a world coin? What country is it from? All of these things matter when figuring the value of a coin.
Assuming the coin is circulated and has no mintmark, retail value is $18.00-$38.00
Assuming the coin is circulated and has no mintmark, the 1891 Morgan dollar is a slightly better date Morgan with retail value of $38.00-$45.00 depending on the actual grade of the coin.
Please post a new question with more information. In 1891 there were 4 denominations of silver coins - dimes through dollars - minted at 4 different mints.
A 1891 U.S. silver dollar is a Morgan dollar. This series of coins were issued from 1878 through 1904 an for the last time in 1921. Assuming the coin is circulated and has no mintmark current values are $30.00-$45.00 depending on the actual grade of the coin.
The coin is very common, circulated examples sell for $17.00-$38.00
The 1891 Morgan Silver Dollar can be seen by using the link to a picture of this coin.
7-18-11>>> Assuming the coin is circulated and has no mintmark, the 1891 Morgan is a high mintage common date, retail values are $36.00-$45.00 depending on the grade of the coin.
The value of a silver coin is always changing because the value of silver is always changing. See the related link below for a silver coin value calculator. This does not give the actual value of the coin but it does give the value of the metal used to make the coin. This is know as the melt value.
There's no such coin. The last Liberty Seated dollars were struck in 1873. The Morgan series started in 1878.
Metal value depends on the purity of the silver and the weight of the coin. Numismatic value depends on the condition of the coin.
There was no 1891 British Two Pound coin issued.
There were no 1891 coins struck.